The present invention relates to a microwave circulator; that is, a nonreciprocal circuit element employing the gyrotropic effect to produce a phase shift which is a function of the direction of energy travel through the device. An etched resonator structure such as a wafer, containing a matching network and connecting leads is provided on one side of the circulator and a ferrite wafer is disposed on the other metallized side of the circulator in a recess made in the metallization, the latter side serving as the ground surface.
The most common circulator structure is the branching circulator. This is a nonreciprocal three-gate structure in which, in the ideal case, high-frequency energy is transported in only one sense of rotation and all gates are matched without reflection to the coupled waveguide system. The circulator may then be used to decouple signal input and output in active dipoles, as a directional line or as a switch.
For some time, such circulators have been produced in integrated form and applied to substrates using printed circuit techniques. The problem in the design of such circulators is the arrangement of the ferrite disc which is part of this component and which is penetrated by a magnetic field in a direction perpendicular to the surface of the substrate.
In the periodical IEEE Transactions on Magnetics, Vol. Mag.-11, No. 5, Sept. 1975, page 1275, FIG. 8, a circulator is shown in which the ferrite disc facing the side containing the conductor structure is inserted into the substrate and has its surface flush with the plane of the substrate. The metal layer disposed on the ground side is applied to the substrate and the ferrite disc in the same plane. This arrangement has the drawback that when there are temperature variations, the ferrite disc or the metal coating of the ground surface, respectively, may be destroyed, because the thermal expansion coefficients of ferrite (10 ppm/.degree. C.) and of the substrate substance (6.6 ppm/.degree. C.) are different.
Moreover, this embodiment requires adherence to very close tolerances during manufacture of the ferrite disc and its recesses and thus makes the process more expensive than other fabrication methods.
The arrangement illustrated in the 1971 Symposium IEEE-GMTT Int. Microwave Symposium Digest, Washington (1971) May, page 79, FIG. 1a, has the same drawbacks. In this embodiment, the ferrite disc is disposed in a recess in the substrate. Although this arrangement has electrical advantages, they do not compensate for the danger of destruction upon the occurrence of differences in temperature. This embodiment also requires that very close tolerances be met during the manufacture of the recess and the ferrite disc.